To reduce the number of analyses and the attendant risk of Type I error, a factor analysis was performed on CNVarea across the 31 electrode sites to find topographic regions of homogeneity that could be reduced to a single score. A principal components analysis followed by varimax rotation yielded two factors that explained most of the variance across the 31 sites. The anterior sites exhibited greater (>.5) loadings on the first factor. The sites around and posterior to the central sulcus exhibited greater (>.5) loadings on the second factor. Average CNV amplitudes within these two scalp regions were significantly different, F(1,157) = 36.4, p<.001. We therefore chose to calculate average area scores representing CNV amplitude within anterior (FP1, FP2, AF1, AF2, F3, F4, F5, F7, FZ, FC2, FC4, FC5, FC6) and posterior (C3, C4, CZ, CP1, CP2, CP5, CP6, P3, P4, PZ, T7, T8, P7, P8, PO1, PO2, O1, O2) regions. These regional amplitudes were analyzed separately.
